The present invention relates to an optical disk driving device for recording or reproducing information on a rotating optical disk by means of an optical system and, particularly, to such a device for storing the optical disk in a predetermined position reliably immediately before the device stops operating.
FIG. 4 is a block circuit diagram of a conventional magnetic disk drive device such as shown in pages 1426 to 1432, Mitsubishi Denki Giho, vol. 46, No. 12, Dec., 1972, wherein reference numeral 40 depicts a linear motor coil for moving a magnetic head (not shown) to an aimed track of a magnetic information storage disk (not shown), and 41 is a speed sensor for magnetically detecting the speed of movement of the linear motor (not shown) driven by the coil 40.
A linear motor control circuit 42 for controls the speed of the linear motor on the basis of a preset reference speed and the output of the speed sensor 41 and provides an output applied to the linear motor coil 40.
Reference numeral 43 is a switch circuit having a selection terminal A connected to a junction between the linear motor control circuit 42 and the linear motor coil 40, 44 is a power source connected to a selection terminal B of the switch circuit 43, and 45 is a capacitor connected to a common terminal C of the switch circuit.
In operation, when the power source 44 is connected in circuit, the common terminal C is connected to the selection terminal B and therefore the capacitor 45 is charged thereby.
At this time, a normal access operation is performed by driving the magnetic head facing the magnetic disk. First, the speed sensor 41 detects the speed of the linear motor and inputs the detected speed to the linear motor control circuit 42. The latter supplies a signal indicative of a difference between the preset reference speed and the detected speed to the linear motor coil 40 so that the detected speed is controlled on the basis of the reference speed. Thus, the linear motor coil 40 drives the linear motor at the preset reference speed and positions the magnetic heas at the aimed or target track of the magnetic disk.
When the power source is disconnected from the magnetic disk device, a carriage mounting the magnetic head is returned from a track of the magnetic disc to a track "00" thereof, and moved to a predetermined storage or reset position. This function is generally called a "retract function".
Under an abnormal situation such as a power source malfunction or a malfunction of the commercial power line, the common terminal C in the switch circuit 43 is connected to the selection terminal A to supply energy stored in the capacitor 45 to the linear motor coil 40 so that the linear motor implements the retract function. Any damage due to contact between the magnetic disk and the magnetic head is thus prevented. A similar retract function is also provided in conventional optical disk drive devices.
FIG. 5 is a side view of an access mechanism of a conventional optical disk drive device. In FIG. 5, an optical information recording disk 1 is adapted to rotate around a rotary shaft 1a and has a spiral track or coaxial tracks thereon with a predetermined constant gap therebetween.
An optical head 2 is adapted to direct an optical beam to a recording surface of the disk and receive reflections for recording and reproducing information with respect to the disk. Reference numeral 3 depicts a carriage for mounting the optical head 2 and moving it to an aimed track address, and 4 a linear actuator magnetic circuit for moving the carriage 3 radially of the optical disk 1. The linear actuator corresponds to the linear motor of the magnetic disk drive device.
Reference numerals 5 and 6 depict inner and outer peripheral stoppers for determining the innermost and an outermost positions of the movement range of the carriage 3, respectively, 7 is an innermost track position accessible by the optical head 2, and 8 is a retract position which is inside of the innermost position 7 and at which the carriage 3 is to be locked.
The positioning of the optical head 2 with respect to the tracks on the optical disk 1 is performed similarly to the magnetic disk drive device. In this case, however, it is necessary to prevent mechanical shocks due to the fact that sensitive optical part such as objective lenses are used, and to lock the carrige 3 mounting the optical head 2 thereon when the device is stopped. Therefore, the optical head 2 is moved to the retract position 8 and stored thereat by the retract function of a capacitor 45.
The retract position 8 is at the end of the movable range of the linear actuator, and it is inside of the innermost position 7 as shown in FIG. 5. Therefore, it is impossible to move the carriage 3 to the retract position 8 by the normal access operation to the tracks on the optical disk 1 because there is no address for the retract position.
Therefore, the carriage 3 is firstly moved to the innermost position 7 for which an address exists by the usual access operation, and is then forcibly moved to the retract position 8 by the charged energy of the capacitor 45.
Due to the fact that, in the retract operation, the capacitor 45 is used to move the carriage 3 from the innermost position 7 to the retract position 8, the capacitor 45 must be large enough to store the energy necessary to achieve such operation, which is usually large when an undesired tilting of the whole device is taken into consideration. This fact makes the whole device large in size. Further, since the carriage 3 is moved to the retract position 8 forcibly, mechanical shock necessarily results which reduces the reliability of the functioning of the optical head 2.